Target Handling and Fluid Systems

Providing adequate cooling for the target at the 5 MW power level of ESS requires distributing the heat over a much larger volume than the few litres instantaneously irradiated by the proton beam. In addition, the amount of radioactivity created in the spallation process must be safely contained both in normal operation and in the case of accidents, in order to avoid damage to the inhabitants living around the facility, to the personnel and to the environment.

Containment of radioactivity

The target monolith will provide two barrier layers of containment against the escape of volatile and airborne radioactive materials, both at normal operation and in case of incidents, and will be continuously vented and filtered. The unavoidable residual escape of radioactive effluents in amounts below the limits authorised in the operational license will be ventilated, collecting these gases from all facility buildings housing equipment including the target.

The parts exposed to the proton beam and the high-radiation environment around the target will have a limited lifetime ranging from a few months to several years, which is short compared with the several decades of ESS operation. These components will also become highly radioactive during operation. Their periodic replacement, handling and storage before disposal will be achieved using remote control and adequate protective equipment, including hot cells and casks at various locations around the target monolith.

The cooling system

The ESS proton beam represents a five-fold leap in power over other neutron spallation sources such that cooling presents considerable challenges. Two cooling systems have been considered. Water has been used to cool previous tungsten targets but could be less effective and safe at the power level of ESS. An effective water-cooled system is likely to be complex and would take longer to license. An inherently safer and simpler-to-license alternative is helium-gas cooling. Helium has not been used for cooling spallation neutron sources before, so there is less experience to build on in the design and development of appropriate engineering systems.